A connecting member such as a fiber optic connector has a plurality of fine holes 12, as shown in FIG. 9, which are formed in one end face 11 of the connecting member and equally spaced by a predetermined pitch P so that the fine holes 12 are arrayed in a row, guide pin insertion holes 13 which are formed on either side of the fine hole array 12, and optical fiber insertion holes which are formed in the other end face 14 opposite to the end face 11 to communicate with the fine holes 12, respectively.
These connecting members are manufactured using a mold, such as the one 20 shown in FIG. 10. The mold comprises a pin mold 25 in which a plurality of pins 21 for forming the fine holes are arrayed in the width direction of the mold, pins 23 for forming the guide pin insertion holes are formed on either side of the pin array 22 of the fine hole forming pins 21, a pin holder 24 supports one end of these fine hole forming pins 21, and the end of the pin holder 24 and one end of the pins 23 for forming the guide pin insertion holes are supported on the pin mold 25 base. The mold 20 further comprises a lower mold 30 in which a positioning member 28 has a plurality of pin receiving holes 26 arrayed to correspond to the fine hole forming pins 21 such that the fine hole forming pins 21 are adapted to be inserted through these holes 26, and another plurality of pin receiving holes 27 configured such that the pins 23 for forming the guide pin insertion holes are inserted in these holes 27. The mold 20 further comprises an upper mold 31 which is used to place above the lower mold 30 to cover the same and accommodate the pin mold 25 therein.
A connecting member 10 is produced as follows: The leading ends 21′ of the fine hole forming pins 21 and the leading ends 23′ of the pins 23 for forming the guide pin insertion holes are inserted in the pin receiving holes 26 for the fine hole forming pins, and the pin receiving holes 27 for the pins for forming the guide pin insertion holes, respectively. Then, from a resin injection nozzle (not shown), a resin composition is injected into the inner space of the mold surrounded by the upper mold 31, the lower mold 30, the positioning member 28 and the pin mold 25 so that the injected resin composition will be hardened therein into a molded product.
The resin composition used for the molding is comprised of a resin or plastic material and a filler mixed in the resin. In the conventional art, the size of filler particles is chosen to be less than the space formed between the fine hole forming pins 21 in order that the resin composition can easily pass through the space between the fine hole forming pins 21. (See for example, Patent Document D1)
Such a fiber optic connector is used to connect optical cables. Typically, for the connection, optical glass fibers having an outer diameter of 125 μm are arrayed with the fiber-to-fiber distance of 250 μm.
The recent development of optical connection technology or “interconnection” technology for optically interconnecting CPU boards requires higher density of the spacing; for example, the fiber-to-fiber distance or pitch of 125 μm has been proposed. To address such high density requirement, the pitch of the fiber optic connector has to be made smaller accordingly.
In general, the use of resin composition containing filler particles of small diameters improves the transfer rate of the resin composition so that a molded product having reduced surface roughness is produced. (Lecture Papers of Plastic Working Spring Lecture Meeting, P 145, 2004 “Development of Transfer Assessment Using Accurate and Fine Mold”)
FIGS. 11 and 12 illustrate frequency distributions of diameters of the filler particles in the resin. FIG. 11 shows a resin composition A in which filler particles of 30 μmφ diameter have the maximum or highest frequency and the largest or maximum filler particle diameter is as large as 100 μmφ. FIG. 12 shows another resin composition B in which filler particles of 30 μmφ diameter have the highest frequency and the largest filler particle diameter is limited to 60 μmφ. FIG. 13 shows transfer rates of molded products using these resin compositions. FIG. 14 shows surface roughness of the molded products using these resin compositions. As seen from FIGS. 13 and 14, the molded product using the resin composition B containing relatively smaller sized filler particles has better transfer rate and better surface roughness than those of the molded product using the resin composition A.
Therefore, it is expected that the connecting member disclosed in the patent document D1 has improved properties in terms of the transfer rate and the surface roughness.
Patent Document D1: Japanese Patent Application Publication 2004-86089